In the step of sealably attaching a base to a fluorescent tube, the base prefilled with an adequate quantity of cement is fitted to an end of the fluorescent tube and is heated locally. This local heating was heretofore performed either by direct heating system in which the tube end was heated directly by a flame of a burner or by indirect heating system in which the tube end was heated indirectly by a heating jig. The direct heating system had, however, a disadvantage in that the flame of the burner tended to be brought into direct contact with the glass tube to damage it and required frequent adjustment. The indirect heating system had likewise a disadvantage in that both heating and cooling had to be performed through the jig and, accordingly, the entire operation was slow and inefficient.